The objective of this proposal is to validate a panel of proposed biomarkers of mammalian aging in animals supplied by the NIA/NCTR biomarker research colony. The specific aims are to apply and evaluate six potential biomarkers as indexes of age- dependent changes in cell physiology in the Fischer 344 rat at 2, 6, 12, 18, 24 and 30 months of age. Ad libitum fed animals will be studied through age 24 months and dietary restricted rats will be studied through age 30 months. The biomarkers are: 1) plasma membrane Ca2+-ATPase ('calcium pump') activity in rat erythrocytes and its in vitro responsiveness to physiological concentrations of thyroid hormone; 2) cytoplasmic content (radioimmunoassay) of calmodulin, a calcium-binding regulatory protein in erythrocytes and dermal fibroblasts; 3) glycosylated hemoglobin content of erythrocytes (mini-ion exchange column); 4) plasma membrane glucose transport (glucose flux) activity in fat pad adipocytes and mononuclear cells; 5) responsiveness, in terms of glycosaminoglycan synthesis, or dermal fibroblasts in vitro to thyroid hormone, glucocorticoid and to various growth factors (epidermal growth factor, platelet-derived growth factor, insulin); 6) microalbuminuria (microgradient gel electrophoresis). Except for glucose flux studies, initial measurements of biomarkers will be followed at 1-to-3 month intervals by repeated assessment in order to estimate reproducibility and determine longitudinal changes in individual animals. Results from ad libitum fed animals will be compared with those from dietary restricted rats whose lifespans are extended. Susceptibility of the Fischer 344 rat to chronic nephropathy requires that glomerular filtration rat (GFR) be monitored and that putative aged-related changes in biomarkers be distinguished from the possible contribution to these measurements of decreased GFR. The collaborating investigators have published their own methods for each of these biomarkers with the exception of glycohemoglobin, and the applicant institution has established laminar flow caging in dedicated nonbarrier rooms in its animal colony for maintaining rodents previously raised in Specific Pathogen Free (SPF) barrier facilities. The advantages of the biomarkers proposed are their nonlethality, minimal invasiveness, relative simplicity and prospect for longitudinal application. Support currently exists for relevance to human aging of the proposed biomarkers.